As a conventional binding device serving as the background of this invention, there is a binding device disclosed in, for example, International Publication Number WO 2004/028828.
This binding device includes: a binding ring; a holding member having a length which allows binding rings to be disposed with a spacing therebetween; an operating member having a surface to which base portions of the respective binding rings are secured such that the binding rings are disposed with a spacing therebetween; and the operating member being movably secured inside the holding member such that the binding rings are secured to the holding member. The binding device includes the operating member, wherein the operating member comprises a pair of operating pieces which move inside the holding member in a longitudinal direction of the holding member, one of the base portions of each of the binding rings being secured to one of the operating pieces, the other base portion of each of the binding rings being secured to the other operating piece, and the binding device includes an opening/closing member which, when the binding rings are opened, moves the operating pieces in the longitudinal direction of the holding member and causes the binding rings to be changed in the opening direction such that the operating pieces are held in the direction approaching the inner surface of the holding member.
Patent Document International Publication Number WO 2004/028828